Are the two audio sources stereo (four total audio signals) or mono (two total audio signals)?
Two stereo output sources (four total audio signals) into one stereo destination: left1 + left2 = left-out, right1 + right2 = right-out ?
IF yes
AND IF you have extra volume available
THEN you can do this with four resistors, no active circuits of any kind.
What are the audio sources? iPhone, MP3 player, 8-track tape, etc.?
What is the headphone? $1.99 ear buds, $1000 Grado, 1970's Koss, etc.?
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